In general injection molded plastic caps for bottles are inevitably associated with certain dimensional fluctuations particularly in the screw thread portion thereof, depending upon the material used and the contraction resulting from cooling after the molding step.
Such a cap, when used in combination with such positioning container as mentioned above, is therefore apt to result in an incompletely air-tight closure in the determined closing position due to the dimensional errors in the screw thread portion, thus often giving rise to leakage of the content.